Disorders of purine metabolism occur in about 5% of the population and may eventually lead to clinical disease in 1%. The clinical manifestations of these disorders range from gout to severe combined immunodeficiency disease. Despite the importance of derangements in this pathway to the pathogenesis of human disease, it now appears that a better understanding of some of those disorders at the most fundamental levels may have even broader implications to the progress of biomedical science. In the present investigation, we will focus on a) defining the nature and consequences of the specific mutations occurring spontaneously in humans which alter the expression of hypoxanthine guanine phosphoribosyltransferase (HPRT) and adenine phosphoribosyltransferase (APRT), b) developing an approach to inserting the HPRT complementary DNA into neuronal cells in culture using a modified neurotropic virus as the vector, and c) elucidating in the brain the normal role of HPRT as well as the metabolic aberrations resulting from its deficiency. During the tenure of this grant we propose to exploit the most advanced scientific techniques and experimental approaches available ranging from the highly sophisticated tools of the basic biochemist to the complex but highly powerful instrumentation utilized by the skilled clinician. Specifically, our approach will utilize a) recombinant DNA techniques involving cDNA cloning and sequencing, construction of useful chimeric plasmids and site directed mutagenesis, b) highly sophisticated methodology at the level of the protein including X-ray crystallography, immunocytochemical localization, and, as necessary, microsequencing and monoclonal antibody techniques, and c) at the bedside, Positron Emission Tomography (PET). Our work on the Regulation of Purine Metabolism in Human Cells has moved over the years from the bedside to the cell to the protein and now to the gene as well as back to the bedside. It is our expectation that these studies will not only substantially expand our information base related to the specific diseases associated with a deficiency of HPRT (Lesch-Nyhan syndrome; Gout) and APRT (2,8 dihydroxyadenine stone disease), but also will provide important information on human gene and protein structure and function as well as on gene transfer particularly in the neurologic diseases.